I. Field of the Invention
This invention relates generally to balloon catheters, and more particularly to a method for fabricating a multilayer balloon composite exhibiting enhanced characteristics attributable to the properties of the individual layers.
II. Discussion of the Prior Art
As an alternative to open-heart, coronary bypass surgery, a technique referred to coronary transluminal angioplasty has been developed following the pioneering introduction of the technique by A. Gruntzig. In carrying out this procedure, a dilatation catheter having an inflatable expander member (balloon) on the distal end thereof is routed through the vascular system to a location within a coronary artery containing a stenotic lesion. Following placement of the expander member across the lesion, a fluid is introduced into the proximal end of the catheter and is used to inflate the expander member to a predetermined relatively high pressure whereby the lesion is compressed into the vessel wall restoring patency to the previously occluded vessel.
It is desirable that the composite expander member exhibit the following characteristics:
1. High burst (tensile) strength;
2. Low radial expansion at elevated pressures;
3. Ease of bonding to a catheter body;
4. Failure characteristics avoiding pinhole ruptures; and
5. Low coefficient of friction.
The Schjeldahl et al. U.S. Pat. No. 4,413,989 owned by applicants' assignee discloses a coronary transluminal angioplasty catheter in which the expander member is formed from polyethylene terephthalate in a drawing and blow molding process so as to provide biaxial orientation to the material. Such PET balloons are found to exhibit the desirable property of high burst strength and relatively low radial expansion when inflated to seven atmospheres or more. However, because the catheter body itself is generally fabricated from a formulation containing silicon rubber, polyethylene, PET or polyurethane, a problem exists when attempts are made to bond the expander member to the distal end portion of the catheter body. The PET polyester balloon tends not to adhere easily to the catheter body especially in a thermal bonding process.
Moreover, experience with polyethylene, PVC and polypropylene expansion members has shown that at relatively high pressures, pinhole leaks form which may create a high velocity jet of inflation fluid capable of perforating the blood vessel when it impinges on the vessel wall. Thus, it would be desirable if the expander member can be fabricated in such a way that it exhibits a controlled mode of failure, i.e., a rapid rupture so that the pressure is released over a significant area in a short time frame.